The NCHT, which registered with the commission in 1980, published a letter on its website, dated 3 May, called "Open letter to all members of the dharmic faiths & members of all British religious traditions". The term "dharmic faiths" refers to Hinduism and several related religions, including Buddhism, Jainism and Sikhism.

The letter, signed by Satish K Sharma, general secretary of the charity, says: "On the basis of a sequence of acts of religious persecution of British Hindus, detailed below, by the parliamentary Labour Party, we confirm that we wholly understand and agree with the sentiment recently expressed by one of our younger volunteers, who stated that ‘British Hindus, Sikhs and Jains voting for Labour is now like turkeys voting for Christmas’."

The letter says both Labour and the Liberal Democrats have pledged that if elected they would immediately introduce legislation that would "effectively introduce a caste system here in the UK".

It does not make clear where this commitment to introduce a caste system is made. Labour’s manifesto does not use the word "caste", while the Liberal Democrat manifesto says that the party would "outlaw caste discrimination".

The letter says that this legislation would be similar to the amendment to the Equality Act 2000 introduced in 2013 by Lord Harries of Pentregarth, a crossbench peer, which specifically outlaws caste discrimination. There are concerns among Hindus and other communities that this would lead to them being targeted with unfair accusations of caste discrimination.

The letter says: "This is NOT a recommendation for members of the dharmic communities to vote for a particular party, but it would be unfair not to recognise that the Conservative Party is the only principal party which has rejected the process whereby this legislation was forced through, and the Conservative Party is the only party which has consistently listened to us and voted against this legislation and whose members are committed to repealing the caste amendment if re-elected."

The letter says that, regardless of the party, Hindus should vote and that not voting would be "adharma", or not in line with religious teaching.

This morning the text of the letter was changed to omit the words "and agree with" in the first paragraph quoted above.

A spokeswoman for the commission said that the regulator's guidance "makes clear that a charity must not give its support to any political party or candidate". She said: "We are aware of the notice posted on the National Council of Hindu Temples’ website and will be contacting the charity to establish the facts of this matter as a matter of urgency. The commission will decide what action, if any, is required once the charity has responded."